Geotechnical Instrumentation

Model 3000 Series

Operating PrincipleThe Model 3000 Load Cell is designed primarily for use

on tiebacks and rockbolts. They may also be used during

pile load tests and for monitoring loads in crosslot struts

and tunnel supports, etc.

In most situations, the Model 3000 is used in conjunc-

tion with bearing plates, positioned on either side of the

load cell.

Where load cells are used to check the load as deter-

mined by the hydraulic pressure applied to the jack,

during proof-testing on tiebacks, rockbolts, etc., the user

should be aware that, due to the annular design and

the many variables in load distribution, the agreement

cannot be guaranteed better than ±15%.

In use, load cells are positioned so that the tensile load

in the tieback or rockbolt produces a compressive load

in the load cell. This is done by trapping the load cell

between bearing plates positioned between the jack

and the structure, either below the anchor plate for

permanent installations or above the anchor plate for

proof-testing.

Advantages and LimitationsThe Model 3000 Load Cell is made from an annulus of

high strength steel or aluminum. Electrical resistance

strain gages are cemented around the outside of the

annulus and connected in a Wheatstone Bridge circuit

so that there is a single mV/V output. Remote sensing

techniques are used to minimize cable effects. Solid load

cells are also available.

An outer shell protects the gages from damage and

‘O’-rings on either side of the gages ensure that the load

cell is fully waterproof.

The cable is attached to the cell through a waterproof

gland. A strain relief, in the form of a Kellem’s grip,

prevents the cable from being pulled out of the cell.

Cables have thick PVC jackets and can be terminated in a

10 pin connector to mate with the GK-502 Readout.

The calibration of annular shaped load cells is very

dependent on the end loading conditions, i.e. on the flat-

ness and thickness of the bearing surfaces and on any

mismatch in size between the load cell and the hydraulic

ram which could cause bearing plates to bend. Calibration

variations of as much as 15% have been observed. For

best accuracy, calibrations should be performed while

duplicating or simulating actual field conditions.

Model 3000 Series Load Cells.

ApplicationsThe Model 3000 Electrical

Resistance Strain Gage Type

Load Cells are used for…

Monitoring loads in tie-

backs and rock bolts in

the walls of excavations

Monitoring loads in steel

arch tunnel supports

Monitoring loads in cross

lot struts

Measurement of loads

during pile testing

Electrical Resistance Type Load Cells

Model GK-502 Readout for use with the Model 3000 Series Load Cells.

Closeup of cable insertion showing Kellems® wire mesh grip.

The World Leader in Vibrating Wire Technology TM Geokon maintains an ongoing policy of design review and reservesthe right to amend products and specifications without notice.

Geokon, Incorporated48 Spencer StreetLebanon, NH 03766USA

1 • 603 • 448 • 15621 • 603 • 448 • 3216geokon@geokon.comwww.geokon.com

©2014 Geokon, Incorporated. All Rights Reserved | Doc. Rev. A.3, 06/14

Rock Bolt

Anchor Nut

Anchor Plate

Load Cell

Bearing Plate

Bearing Pad

Signal Cable

Geotechnical Instrumentation • Made in the U.S.A.

Model Number

Instrument CableKellems Grip

Cover

Cover Screw

(top view) (side view)

OD (Outer Diameter)ID (Inner Diameter)

Pile

LoadCell

HydraulicJack

BearingPlate

Reaction Frame

System ComponentsSignals from the load cell are transmitted to the readout

location by means of a multi-conductor shielded cable,

which may be armored for extra protection. Kellems

grips prevent the cable from being pulled from the load

cell. Larger size load cells are supplied with lifting lugs.

To minimize eccentric and uneven loading, the use of

the thick machined-flat bearing plates and centralizer

bushings (where necessary) are recommended.

Bearing plates should be machined flat and large

enough to totally cover the load bearing surface of

the load cell. The thickness is related to the load cell/

hydraulic jack size mismatch: the greater the size

disparity the thicker the bearing plate. Typical thickness

ranges from 25 to 75 mm.

If the size of the tie-back or rock bolt is more than

20 mm smaller than the internal diameter of the load

cell, then centralizer bushings are recommended.

Readout of the Model 3000 Load Cells is achieved

using the Model GK-502 Readout or with the

Micro-800/1000 Dataloggers.

Technical SpecificationsRated Capacities1 100 to 10,000 kN

Over Range2 150% F.S.

Resolution 0.025% F.S.

Accuracy 3 ±0.5% F.S.

Output 1.5 to 2.5 mV/V @ F.S.

Temperature Range4 −20°C to +80°C

Cables Multi-conductor shielded pairs with PVC outer jacket

Internal Diameters1 solid, 25, 50, 75, 100, 125, 150, 200, 250 mm

1Other capacities and diameters available on request. Calibrations that exceed Geokon’s NIST traceable capacity of approximately 10,675 kN are subcontracted to an accredited testing laboratory.

2With no calibration shift.3Established under laboratory conditions. System accuracy depends on end loading conditions.

4Other ranges available on request.

Model 3000 Series Load Cell components.

Load cells used in pile test.

Load cell used to monitor performance of tie-back in excavation.